Clutch-brake steering mechanism for tractors

ABSTRACT

Clutch-brake steering unit having hydraulically actuated cylinders for controlling same to control rotation of a track-drive sprocket in a crawler tractor. Specifically a clutch cylinder and a brake cylinder provided in the unit have an inlet-outlet port in common, and are so arranged on a spring-applied-brake, hydraulically-applied-clutch basis that a single pressure signal in the inlet-outlet port alternately operates the cylinders to apply the brake and release the clutch, to apply the clutch and release the brake, or by proper modulation to partially engage either, i.e., slip the clutch or drag the brake to intermediate degrees as desired.

This is a division of application Ser. No. 561,119, filed Mar. 24, 1975now U.S. Pat. No. 4,015,619 through intervening Ser. No. 708,956 nowU.S. Pat. No. 4,164,276, and Ser. No. 10,568, now U.S. Pat. No.4,308,893, filed respectively on July 26, 1976 and on Feb. 9, 1979.

This application relates to clutch-brake mechanism for use in vehicleswhich are steered-by-driving. It more particularly relates to the leftand right clutch-brake steering units for a crawler tractor.

It is an object in connection with steering mechanism according to ourinvention, to provide an alternately acting, hydraulically actuatedclutch-brake unit so arranged that braking is automatic (spring applied)upon failure of hydraulic pressure, thus affording fail-safe braking.

An object in line with the preceding objective is to provide aclutch-brake unit in which a clutch and a brake are siamese-connectedfor pressure actuation of same, and in which a single signal istherefore usable for control pressure both for the clutch and for thebrake in the unit.

A further object is to provide a metering valve for controlling thesignal pressure, also provide an inlet-outlet port to which clutch andbrake cylinders are connected in common and controlled by the meteringvalve as the signal pressure is applied or released, and additionallyprovide correlated sets of springs on the clutch and brake causingengagement of each cylinder to be cushioned by delayed pressure-changeowing to the fact that the volume of the cylinder of the other isundergoing a metered change because of the metering valve's restrictivecontrol over the common inlet-outlet port.

According to practice in the past in connection with some clutch-brakesteered crawler tractors, the steering clutch has been operated througha controlled rate-of-rise valve to cushion clutch engagement. Similarly,the companion brake has been operated through a second valve and, if themanner desired has been to cushion the brake engagement, the secondvalve has likewise afforded controlled rate of pressure rise in thebrake cylinder. It has therefore been the practice to have some accuratecoordinating means providing for precise coordination of operation ofthe two clutch and brake valves, which only slightly overlap inoperation so as to insure appreciable releasing of the clutch prior tostarting to engage the brake, and vice versa. Disadvantages and inherentcomplications have arisen because of the need for special rate-of-risevalve control and coordination of the valve operations in controlling orslowing rate of pressure rise in the cylinders.

Our invention materially reduces, if not substantially eliminating, theforegoing disadvantages and complications, as will now be explained indetail. Various features, objects, and advantages will either bespecifically pointed or become apparent when, for a better understandingof our invention, reference is made to the following description takenin conjunction with the accompanying drawings which show a preferredembodiment thereof and in which:

FIG. 1 is a schematic view, in top plan, of a crawler tractor embodyingour hydraulically actuated, clutch-brake invention;

FIG. 2 is a partially schematic, cross sectional view of ourclutch-brake mechanism and hydraulic control circuit therefor;

FIGS. 3 and 4 are graphs showing the desired pressure-time tracesinvolved in achieving respective cushioned clutch application andcushioned brake application; and

FIGS. 5, 6, 7, and 8 are partly schematic, cross-sectional views of asteering valve, showing it in various positions in its operation in thehydraulic control circuit of clutch-brake mechanism.

More particularly, in FIG. 1 of the drawings, a crawler tractor 10 isshown having undercarriage structure including right and left endlesstrack assemblies 12 and 14, having a front mounted engine 16, and ahaving a chassis, not shown, supported on the undercarriage structureand supporting the engine 16. The undercarriage structure furtherincludes at its respective sides right and left front idler wheels 18and 20 and right and left track drive sprockets 22 and 24.

The power train from the engine 16 of the tractor includes athree-speed, reversible power shift transmission 26, a rear main frame28 holding the steering mechanism, and suitable interconnections in thepower train whereby the sprockets 22 and 24 receive their drivingtorque, as from a right final drive 30. More specifically, a torqueconverter 32 interconnects the engine 16 and the power shifttransmission 26. Meshing bevel and crown gearing 34 interconnects thetransmission 26 and the rear axle 36 of the tractor, and a rightsteering clutch-bake unit 38 controls power rotation or braking of theright final drive 30 which is supplied with torque by the rear axle 36.

For purpose of hydraulic control over the steering mechanism in the rearmain frame 28, the tractor 10 has a steering valve assembly 40 and, forthat purpose, the steering valve assembly has operator-operated handlevels including a right steering lever 42 connected to a right-steerspool valve 44 included in the valve assembly 40. A brake pedal 46 isconnected to a brake spool valve 48 included in the valve assembly 40.

The steering valve connections are omitted from FIG. 1 forsimplification, but receive the usual hydraulic fluid for theiroperation from a rotary pump 50 driven by a meshing pinion and gear 52which are connected to the output side of the torque converter 32. Aregulator valve 54 which is teed to the output side of the pump 50 has aconstant setting so that pressure in the output line 56 will beessentially constant, e.g., 270 psi (18 atmospheres) under varying pumpspeeds.

The steering controls and drives in the tractor 10 are essentiallysymmetrical, thus further including, for the left side, a secondsteering lever 42-2, a second steering valve 44-2, a second clutch brakeunit 38-2, and a second final drive 30-2.

In operation of the tractor 10, torque in the power train from theengine 16 is applied through the torque converter 32 to the power shifttransmission 26 and gearing 34, which drive the rear axle 36 at a speedand in the direction selected. Line pressure from the line 56 is appliedwith appropriate modulation by the steering valve assembly 40 to theclutch-brake units 38 and 38-2 so that the operator can cause thesprockets 22 and 24 to rotate the endless track assemblies 12 and 14 atthe same speed for straight line drive in either direction, or atdifferent speeds for power turns or braked turns, either left or rightforwardly, or left or right rearwardly.

STEERING MECHANISM--FIG. 2

In accordance with the arrowed path appearing in this figure, power flowfrom the transmission, not shown, follows along a propeller shaft in thepath of an arrow 58 into the bevel and crown gearing 34 so as to beconducted laterally by the rear axle 36 in the opposite directionsindicated by a double headed arrow 60. In the right direction, forexample, lateral power flow from the axle and right steeringclutch-brake unit 38 is in the direction of an arrow 62, through bullgearing 64 and the right final drive 30, thence into the right trackdrive sprocket 22. More particularly, except for a radial flange 66integrally carried by the axle adjacent its right end, the axle 36 whichis hollow is generally symmetrical when one end is compared to theother. The axle 36 is journalled for rotation in a clutch-brake housing68 by means of a span of bearings including a tapered roller bearing 70illustrated. Longitudinal passages in the axle 36 include separate,oppositely extending hydraulic passages 72 and 74 which are parallel tothe hollow interior 76 thereof. The referred to radial flange 66 at itsperiphery carries a crown gear 78 meshing with the bevel pinion of thegearing 34 and driving the axle 36 through a desired reduction gearratio.

For brevity's sake, only the right steering clutch-brake unit 38 isherein illustrated and described. The axle 36 has a counterbore 80 inthe end which communicates with the hollow interior 76 and in which ashort extension plug 82 is tightly press-fitted. Intersectinglubricating passages 84 which are normal to one another communicate withlubricant supplied into the hollow interior 76 so as to conductlubricant through the plug 82 to the unit 38.

A right brake piston 86B which carries seals cooperates with a brakebacking plate 88 to define a sealed right brake cylinder 90B. The brakebacking plate 88 is fixed in the clutch-brake housing 68 and carriesbrake disk splines. The brake piston 86B is hydraulically retracted tofull back disengagement as illustrated by means of the cylinder 90B andis spring applied by means of a set of brake springs 92 pressingthereagainst which seat at their opposite end against abutments in thehousing 68. In one physically constructed embodiment of the spring 92,their spring rate was such that they just began to overcome opposingpressure and started to collapse the cylinder 90B when the pressure inthe latter dropped to 165 psi (11 atmospheres). From their fullyexpanded position, the springs 92 started to collapse when the pressurein the brake cylinder 90B rose to 100 psi (7 atmospheres).

A right clutch piston 94C in the clutch-brake unit 38 cooperates withthe lateral or outer face of the radial flange 66 of the axle 36 todefine a right clutch cylinder 96C. The piston 94C is operated so as tobe spring-released by a set of clutch springs 98, and is pressureapplied to full clutch engagement as illustrated by the clutch cylinder96C. The piston 94C through its movement applies a pressure plateportion 100 thereof which has a larger diameter than the piston portionand which constitutes the radially outer periphery of the piston 94Citself. In one physically constructed embodiment of the invention, thespring rate of the clutch springs 98 was such that they initiallystarted to expand when the pressure in the clutch cylinder 96C haddecreased to 100 psi (7 atmospheres). From their expanded position offull travel, the set of clutch springs 98 started to compress when theclutch pressure in cylinder 96C rose to 50 psi (3 atmospheres).

A bolted on clutch backing plate 102 is affixed to the periphery of theaxle flange 66 and is formed with a set of clutch disk splines. A clutchbrake output member 104 common to the clutch and brake carries a set ofdisk splines 106, and the splines 106 cooperate with the splined brakebacking plate 88 and clutch backing plate 102 for friction engagingpurposes by mutually carrying a set of brake disks 108B and a set ofclutch disks 110C of standard construction. The common output member 104is independently rotatably mounted by means of a bearing 112 on the axleextension plug 82 which, through the lubricant passages 84, provideslubricant for the bearing. A clutch brake output shaft 114 is bolted tothe common output member 104 and transmits torque in the direction ofthe arrow 62 so as to drive the bull gearing 64 through aspline-carried, quill shaft interconnection 116.

The bull gearing 64 is connected through a shaft 118 to the sun gear 120of a planetary gear set. The planetary gear set further includes apinion carrier 122 and a ring gear 124 which is fixed owing to itsinterconnection to a fixed main case 126 by means of a toothed plate128. A set of planet pinions 130 on their common carrier 122 meshesalong an inner pitch circle with the sun gear 120 and meshes along anouter pitch circle with the ring gear 124, so as to impart through thecarrier 122 a reduced gear speed to a rotationally supported casting 132carrying the sprocket 22 and affixed to the carrier of the final drive30.

STEERING OPERATORS--FIG. 2

Hand and foot operation as utilized according to the illustrated examplein FIG. 2, and the operators comprise the brake pedal 46 and the leftand right steering levers 42-2 and 42. The brake pedal 46 has a bottompivot 134 and through a clevis connection to a mid-pin 136 on the pedal,the pedal 46 operates a pull connection 138 to pull the foot brake spoolvalve 48 to a braking position as opposed by a spool valve return spring140. The brake-applied position is shown in broken line in FIG. 2.

The steering levers have a mid pivot such as illustrated at 142 for theright steering lever 42 and, as shown in FIG. 2, the connection from thesteering lever 42 is schematically illustrated at 144 whichinterconnects with the spool valve 44 to pull it into the brakedposition as opposed by a spool valve return spring 146. Or especially ascan be seen in FIG. 2, the connection to the left steering lever 42-2 ismore fully illustrated to include a pull link 147, having a front clevisconnection to a bottom pin 148 on the lever 42-2, a rear clevis having aconnection to a top pin 150 on a bottom-pivoted link 152, and a pulllink 154 connected to a mid-pin 156 on the link 152 and connected to theleft spool valve 44-2 so as to pull the latter against the resistence ofa spool valve return spring 158.

STEERING HYDRAULICS--FIG. 2

In the hydraulic circuit as shown according to this figure, the line 56carrying line pressure splits up at 160 into a metering valve branch 162connected to a pressure port 164 in the steering valve assembly 40 andinto a second branch 166 connected to a signal pressure port 168. A oneway towing valve 170 has a tee connection 172 with the metering valvebranch 162 and opens in the direction of the tee. Intermediate the splitup 160 and the tee 172, a one way valve 174 is connected in the branch162 and opens in the direction of the tee 172. The pressure ports 164and 168 are in the inlet side of the steering valve assembly 40 and areconnected to a longitudinal first bore 176 in the assembly by,respectively, a valve passage 178 and a bore groove 180, and a valvepassage 182 and a bore groove 184.

Another bore groove 186 is the means by which a drain port 188communicates with the bore 176 and also communicates with an upwardlydirected passage 190 in the valve assembly 40. A brake valve bore 192which is parallel to the valve bore 176 includes a bore groove 194. Thedrain port 188 communicates through a downwardly extending passage 196and the bore groove 194 with a drain line 198.

Disposed in mutual end-to-end abutting relationship the spool valve 44and a metering spool 200 share the right-steer bore 176. Adjacent themetering spool 200, an inlet-outlet port 202 communicates therewiththrough a bore groove 204. The inlet-outlet port 202 also communicateswith the clutch cylinder 96C in a path including a valve passage 206, abore groove 208 in the brake bore 192, and a right clutch line 210C,thence through the right axle passage 72 into the right clutch cylinder96C.

A spool 212 adjacent the end of the brake spool valve 48 communicateswith the bore groove 208, and controls flow therefrom to the right brakecylinder 90B in a path including a bore groove 214, thence through aright brake line 216B into the brake cylinder 90B.

In addition to the valve bore 192 parallel thereto, the bore 176 has asecond bore 176-2 formed parallel thereto in the steering valve assembly40. The second bore includes the spool valve 44-2 and a metering spool200-2 and communicates in similar way by means including a line 210C2and 74, and also a line 216B-2, with a respective left clutch cylinder96C2 and left brake cylinder 90B2.

In the steering valve assembly 40, spring chambers 218, 220 and 222 oflarge diameter receive the respective smaller diameter spool valves 44,44-2, and 48, and communicate through a common, side groove 224 with adrain 226.

The present fail-safe braking system, under which the systemautomatically and fully sets the steering brakes upon loss of hydraulicpressure in the system, necessitates provision of a tow valve, now to bedescribed.

TOW VALVE--FIG. 2

Through a branch 228, line pressure from the line 56 flows into theactuating pressure chamber 230 at one end of the valve bore in a towvalve 232. A slidable valve spool 234 therein includes apressure-movable end land 236, an intermediate land 238, and a land 240at the hollow, right end of the spool 234. The two valve 232 isinterposed in the right clutch line 210C so that the line passes througha pair of longitudinally spaced apart bore grooves 242 and 244 which areinterconnected by a bore passage 246.

At the opposite end of the spool 234 from the chamber 230, a returnspring 248 yieldingly cooperates with the actuating line pressure bycollapsing to allow the spool to move from the broken line position intothe position as shown by the solid lines 234 in FIG. 2. So under theaction of line pressure, the valve 234 allows the grooves 242 and 244 tocommunicate through the bore passage 246, thus directing clutch pressurefluid in the clutch line 210C in the way desired. At the same time,another bore passage 250 allows similar communication in the secondclutch line 210C2, in response to line pressure in the actuating chamber230. Under these circumstances, the end land 236 blocks off linepressure so as to confine it to that chamber 230, and presents thepressure-moveable end area of the spool 234.

TOWING--FIG. 2

In a towing situation of the tractor, there is no line pressure and so,separately, external pressure must be introduced into the system.Pressure, of course, if present generally throughout the system wouldtend in an unwanted manner to apply the hydraulically applied clutch,and yet local pressure properly confined is necessary in order torelease the spring applied steering brakes of the vehicle.

The status existing for emergency towing will be that the lines areunder no pressure and that the return spring 248 of the tow valve 232 isholding the valve spool 234 in the emergency, broken line positionshown.

Emergency fluid introduced under pressure through the one-way valve 170,such as chassis grease pumped in by a hand lubricant gun, will bepevented by the one-way valve 174 from making escape and will be forcedto flow through a path including the pressure port 164, passage 178, theright metering spool 200 in its open position as shown in solid lines inFIG. 2, the bore groove 204, and the right inlet-outlet port 202. Thepath of fluid flow further includes the valve passage 206 and the groove208 of the bore 192 where the path splits up. That is to say, part ofthe path of fluid flow includes the bore groove 214, the brake line216B, and the brake chamber 90B as desired. Also, the rest of the fluidflow path includes the bore groove 208, the tow valve bore groove 242,and the tow valve land 238 which intervenes and blocks the clutch line210C so that the right clutch cylinder 96C receives no pressure andremains disengaged.

Accordingly the right brake becomes fully released as illustrated inFIG. 2 and the clutch stays released to allow the vehicle to be towed.

Likewise, the seconsd brake cylinder on the left side 90B-2 becomesreleased and the second clutch cylinder on the left side 96C2 staysreleased, but the paths and fluid operation are not detailed forbrevity's sake.

ALTERNATIVE ACTION

The foregoing is the only exception to the general rule. The generalrule is that the clutch and brake on the right side of the tractor actsolely in alternation to one another and the clutch and brake on theleft side act solely in alternation to one another. For example, underlow or moderately low pressure in both hydraulic circuits of the system,the clutches will remain disengaged whereas the brakes either will befully engaged or will drag to the proper degree.

On the other hand under high or moderately high hydraulic pressure, theclutches will be fully engaged or will slip to the degree desired, whilethe brakes will stay released from engagement.

SINGLE CONTROL PRESSURE

From the foregoing, and with specific reference to the inlet-outlet port202 of FIG. 2, it is evident that a single control pressure applied toan inlet-outlet port 202 will, depending upon its value, set the tractorin selective conditions for, respectively, full braking, brake dragging,no clutching or braking, clutch slipping, and full clutching without"fight" between a clutch on one hand and the brake on the other. Thisinherent coordination makes for a significant simplification of control.

LIGHT/HEAVY SPRINGS

Typical for both sides of the tractor, the spring force of the brakesprings 92 for the right side is the range of about 100-165 PSI (7-11atmospheres) at the extremes of travel allowed the springs. For theclutch springs, the spring force at 98, for example, is in the range of50-100 PSI (3-7 atmospheres) at the extremes of clutch spring travel.These figures are ones equivalent to, and in terms of, the actualhydraulic system pressure, and it will be seen that one set of springswill have completed its travel just when the other set of springs beginsits travel.

Thus if we increase the hydraulic pressure from 50 PSI (3 atmospheres)to 165 PSI (11 atmospheres), the clutch springs immediately begincontracting travel and complete their movement at 100 PSI (7atmospheres) so as to remove the clutch disk take-up travel and bringthe individual clutch disks into initial engagement, that is, justmaking contact but with no pressure of engagement thereupon. Immediatelyafter the 100 PSI (7 atmospheres) is exceeded in this system, andcontemporaneously with pressure of engagement starting to be applied tothe touching clutch disks, the brake springs begin collapse so that theresultingly separating brake disks, e.g., disks 108B which are no longerunder any residual spring contact pressure, are allowed to restore theirnormal disk take-up travel by freeing themselves from contact and thedisengagement continues to 165 PSI (11 atmospheres) when the brakesprings reach their full extent of contracting travel as shown in FIG.2.

The reverse order is also true because, with decreasing circuitpressure, the brake springs 92 expand for the principal portion of theirtravel as hydraulic pressure drops from 165 PSI (11 atmospheres) to 100PSI (7 atmospheres). Then as the decreasing pressure continues droppingbelow 100 PSI (7 atmospheres), pressure of contact building up in thebrake springs is exerted on the brake disks while the clutch disks 110C,which are under no contact pressure, are freed from one another and fromthe pressure plate 100 as the clutch springs 98 expand to the fullextent of their allowed travel. The clutch spring travel is completed atthe point of a pressure drop to 50 PSI (3 atmospheres) in the hydrauliccircuit.

Although we can doubtless attach significance to the separate andsuccessive sequencing of the spring sets because of inherently insuringno clutch-brake "fight", there is some deeper significance attached tothe sequencing from coodinated spring rates, because of inherentcushioning in hydraulically setting the brakes and engaging andclutches, now to be explained.

CUSHIONING OF CLUTCH--FIG. 3

A desired pressure-time relationship is graphed in this figure leadingup to full clutch engagement, and an illustrative curve is showncomposed of connected linear segments and denoted by a, b, c, d, e, f,and g. The curve segment ab represents zero pressure maintained in thehydraulic circuit by the metering valve, not shown. When the meteringvalve is hydraulically shifted into its clutch-fill position, pressurerise is practically instantaneous as illustrated by the curve segment bcwhereas the segment cd denotes a slow rate of hydraulic pressure riseoccurring throughout the entire spring travel range of the clutchsprings, not shown. That is to say, spring travel of the clutch springstoward full spring compression means that the clutch cylinder, notshown, is filling with progressively increasing volume and thereforereadily accommodating the metering valve flow so that the pressure risesonly gradually. At the point d, the brake disks are in contact under nocontact pressure and the clutch disks will have initially establishedcontact but under no contact pressure.

Novelty is felt to reside in the situation represented by the curvesegment d e. In that situation simultaneously with contact pressure onthe clutch disks being initiated and progressively increasing, the brakesprings, not shown, are undergoing their entire range of travel and animportant function is transpiring. The important function is that volumein the brake cylinder, not shown, is progressively enlarging and thusreadily consuming the metered fluid flow from the metering valve, thuslimiting the pressure rate of rise to the desired slow rate.Accordingly, clutch contact pressure rises linearly at slow controlledrate, rendering initial engagement of the clutch soft and free fromabrupt shock. Cushioned engagement of the disks means appreciablyreduced wear on their friction engageable surfaces.

The operation represented by the curve segment ef is final pressureapplication to the clutch disks which follows at a fast rate of rise inpressure for complete clutch engagement; practically no clutch slip isallowed during this operation. The completed engagement is representedby the curve segment fg, with the steering clutch involved being fullyengaged for solid 1:1 drive at one side of the vehicle and the companionbrake being fully disengaged so as not to interfere.

CUSHIONING OF BRAKE--FIG. 4

A pressure-time relationship is graphed in this figure illustrative ofthe events culminating in full spring-applied brake engagement, and theillustrative curve is composed of interconnected linear segments and isdenoted h, j, k, l, m, and n. The curve segment hi represents thehydraulic system at one side of the vehicle being under full pressure asdirected thereto by the metering valve on that side, not shown. Shift ofthe metering valve into a position allowing metered escape of thehydraulic fluid from the system is represented by the curve segment ij,illustrating a somewhat instantaneous or abrupt decrease of pressure inthe system. Full travel of the brake springs, not shown, due to theirselected spring rate, is represented by the curve segment jk. That is tosay, the brake springs expand over their principal range of travel andeffective volume of the brake cylinder progressively decreases. Theeffect of the emptying brake cylinder is that the rate of pressure dropis comparatively slowed down as the outflow from the cylinder makes itway through the metering valve, not shown. And upon reaching the point kon the curve, the condition as reflected at that point dictates that thebrake is in the status of having a fully collapsed cylinder and thebrake disks are in contact but under no pressure, whereas the clutchcylinder still has the status of being in a full condition but theclutch disks, not shown, are in contact under no contact pressure.

Novelty is felt to be present throughout that operation represented bythe segment kl of the curve. Throughout that operation, decreasingcylinder pressure in the fully extended clutch cylinder, not shown,allows the clutch springs, not shown, to collapse the cylinder throughtheir entire range of travel represented by the curve segment kl. Butescaping fluid from the emptying clutch cylinder requires an interval tomake its way through the metering valve, not shown, and so the rate ofpressure decrease is reduced during initial application of the springapplied brake. Brake disk pressure is therefore slowly applied by thesprings and a soft gradual brake engagement interval ensues. Cushionedengagement of the disks means significantly reduced wear on theirfriction engageable surface.

The curve segment lm represents full application of the brake underbrake spring pressure following collapse of the clutch cylinder. Thefinal pressure reduction represented by the segment lm is at a rapidrate and brings on the brake application at full spring pressure.Thereafter, the full-brake application interval is represented by thesegment mn on the pressure-time curve. The brake is therefore fully setat the vehicle side concerned, and the companion clutch is fullydisengaged so as not to interfere.

MODULATION

Between the pressurization condition of full line pressure, whichobtains in the system when maintaining full clutching as reached in FIG.3, and the pressurization condition of 0 drain pressure, which obtainsin the hydraulic system when maintaining full braking as reached in FIG.4, there lies an infinity of modulated pressures falling in theintermediate range. The steering pressure, right, and the steeringpressure, left, in the tractor are independent of one another and,irrespective of what exists on the left side, for example, the steeringpressure on the right side controlling the right drive sprocket can befixed at any point in the intermediate range, or at either extreme ofpressurization, or can be undergoing a raising or lowering of pressureseither in some sequence with one another or as an isolated instance.

According to our invention, the set value or the changing value ofsteering pressure is controlled with great precision and exactitude bythe means which we provide for that purpose, as will now be explained.

RIGHT SPOOL VALVE 44--FIG. 5

The right-steer valve 44 appearing in this figure: carries, proximately,a drain spool 252 adjacent the spring chamber 218; carries, distally, anend spool 254; and, separated by a valve groove 256 from the end spool254 and separated from the drain spool 252 by the annular recess 258formed by a reduced portion of the spool valve, the valve carries apressure spool 260. To varying degrees depending upon the longitudinalposition into which the spool valve 44 slides in the right bore 176, theexterior of the drain spool 252 variously communicates with the springchamber 218 which is at drain pressure, and so, likewise, does a doublehelix 262 which is grooved into the spool exterior. Similarly, a doublehelix 264 which is grooved into the exterior of the pressure spool 260communicates variously with line pressure from the bore groove 184 whichis supplied by the signal pressure port 168 previously described. Thedouble helices 262 and 264 have uniform groove depth, uniform groovesize, and uniform helix angle so that the resulting orifice which eachhelix forms with the closing surface of the valve bore 176 has constantrate of pressure drop along its length after the standard manner ofaccurate hydropotentiometers.

A signal pickup port 266 formed in the valve in the base of the annularrecess 258 communicates through a radial passage drilled in the valveand an interconnecting longitudinal passage 268 with an intervalvechamber 270 defined in the bore 176 between the metering spool 200 andthe end spool 254 of the right-steer spool valve 44. In itscommunicating function in the solid line position of the valve 44 asshown in FIG. 5, the signal pickup port 266 will cause the intervalvechamber 270 to be pressurized at line pressure being introduced by thepressure port 168 through the valve passage 182 and the bore groove 184.The orifice defined by the double helix 262 on the drain spool 252 willbe subjected to the full pressure drop from line pressure in the annularrecess 258 to the drain pressure in the spring chamber 218.

A light pull exerted on the spool valve 44, shifting it in a directionslightly to the right as viewed in FIG. 5, will cause the annular recess258 to be isolated from the full line pressure of the bore groove 184,and a portion of the orifice defined by the double helix 264 will becomeactive in supplying the signal pickup port 266 with pressure of slightlyreduced value. At the same time, a portion of the orifice defined by thedouble helix 262 will become inactive where the double helix enters intothe drain chamber 218, rendering the pickup the port definitely at anintermediate point in the effective overall orifice length. Furtherpressure-reducing shift of the spool valve 44 to the right will causethe signal pickup port 266 to slide to a position more nearlyapproaching the drain pressure and therefore supplying the intervalvechamber 270 with a like reduced pressure.

Finally, shift of the spool valve 44 to its extreme of rightward travelwill place the signal pickup port 266 in communication directly withdrain pressure, thereby establishing drain pressure in the intervalvechamber 270. In this manner, the pressure of intervalve chamber 270 canbe accurately fixed or accurately varied among line pressure and drainpressure, and an infinity of accurately-held pressures in anintermediate range between maximum and minimum.

RIGHT METERING SPOOL--FIG. 6

The metering spool 200 as illustrated in this figure has a centersection of reduced diameter which defines a bore passage 272 and whichintegrally interconnects a solid land 274 and a hollow land 276 of thespool 200. An actual-pressure pickup port 278 in the reduced centersection communicates externally through the bore passage 272 and thebore groove 204 with the right inlet-outlet port 202, and communicatesinternally through a radial passage and a longitudinal passage 280 inthe hollow land 276 with a spring chamber 282 which is at an oppositeend of the spool 200 from the intervalve chamber 270, previouslydescribed.

Adjacent the reduced diameter center section of the spool 200, the solidland 274 has a series of control orifices formed by metering slots 284in the shoulder thereof; in an extreme position of the metering spool200, in the rightward direction as viewed in FIG. 6, the slots 284 withcommunicate with the valve groove 186 which is at drain pressure, andthe actual-pressure pickup port 278 and bore passage 272 will thereforecommunicate drain pressure to the spring chamber 282 and to theinlet-outlet port 202. The opposite extreme position will now bedescribed.

Adjacent its juncture with the reduced diameter center section of thespool 200, the hollow land 276 has a series of control orifices formedby metering slots 286 in the shoulder thereof. In the solid lineposition of the spool 200 as shown in FIG. 6, the metering slots 286 areout of communication with line pressure, but these slots progressivelyprovide communication with line pressure as the spool 200 shiftsleftwardly as viewed in FIG. 6. Thus a metered amount of line pressureup to full line pressure can be communicated from the pressure port 164through the valve passage 178 and bore groove 180, through the meteringslots 286 for ultimate communication with the inlet outlet port 202 andthe spring chamber 282 at one end of the spool 200. A weak spring 288which is in the hollow interior of the land 276 and which seats on anend plate 290 of the steering valve assembly 40, lightly biases thespool 200 in the direction of the opposing much stronger valve returnspring 146; the light spring 288 serves, among other things, to preventthe metering spool 200 from drifting when it is depressurized at 282 andout of physical contact with the end spool 254 of the right-spool valve44.

SIGNALING-METERING--FIG. 6

The first bore 176 and the spool elements therein have the conduit 178connecting high pressure thereto from the pressure port 164 and passage178 into the bore groove 180, have the conduit 182 connecting highpressure thereto from the signal-pressure port 168 and passage 182 intothe bore groove 184, have the conduit 194 and 196 connecting the lowpressure of drain thereto leading to the drain line 198 and leading fromthe drain port 188 and the bore groove 186, have conduit 208 and 206connecting the inlet-outlet pressure thereto from the right clutch line210C and the right brake line 216B, bore groove 214, a bore passage 292into the inlet outlet port 202 and bore groove 204, and have conduit 224formed by side grooves in the spring chambers 218 and 222 connectingdrain pressure thereto from the drain conduit 226 to the drain spool 252of the right-steer spool valve 44.

By controllably connecting two of the high pressure and low pressureconduits just described, the pressure and drain spools 260 and 252 ofspool valve 44 precisely set the signal pressure at a desired value inthe intervalve chamber 270, and the metering spool 200 at its endadjacent the intervalve chamber 270 is exposed to that pressure becauseof the latter's communication thereto through the signal pickup port 266and longitudinal passage 268. As already indicated, the signal pressureestablished by the valve 44 varies between the high and low pressureconduit from a maximum to a minimum proportionally in accordance withthe effective length of orifice defined by the double helices 264 and262 on the spools 260 and 252.

The control orifices formed in the metering spool 200 by the sets ofmetering slots 286 and 284 vary in size and effective fluid handlingcapacity depending upon how much each set of orifices projects at theend beyond the adjacent end of the bore passage 272. Thus, eachparticular longitudinal position of the spool 200 establishes therelative rate of inflow of pressure fluid and outflow of drain fluidthrough the ends of the bore passage 272, accordingly establishing thepressure of inlet-outlet port 202 between the high and low pressureconduits from a maximum to a minimum.

The metering spool 200 stabilizes in its position at the point wheninflow through slots 286 into passage 272 and the outflow therefromthrough slots 284 equalize. At that point, the pressure in the springchamber 282 which is at one end of the spool 200 and which equalsinlet-outlet pressure, is also essentially equal to the signal pressurein the intervalve chamber 270. Or more generally, actual inlet-outletpressure in chamber 282 equals desired pressure set in the chamber 270,if the minor bias of the light spring 288 be ignored, which it can befor our principal considerations.

It is primarily, of course, the strategic location and arrangement ofpickup ports 278 and 266 and longitudinal spool passages 280 and 268 inthe valve elements which makes it possible to have these elementscompactly arranged so as to fit end-to-end in the bore 176 slidablyreceiving same in common. These elements are totally unlike in functionas they mutually relatively move in their bore, and they have a strictmaster-slave relationship. The valve 44 is the element serving asexact-static-pressure-dictator and position-dictator, and the spool 200serves as automatic followup element to take a corresponding satisfied,dictated position in the bore.

FULL CLUTCHING ON RIGHT--FIG. 5

Similarly occupying the full clutching position as shown for the leftspool valve 44-2, the right spool valve 44 is shown in this figure in aposition supplying line pressure to the right clutch cylinder 96C and,likewise, to the right brake cylinder 90B. In other words, full pressurefrom the line 56 leads in a path through the valve 174 the line 162,pressure port 164, passage 178, bore groove 180, control orifices 286,bore passage 272, bore groove and inlet outlet port 204 and 202, passage206, bore groove 208, and thence in split branches one way throughclutch line 210C and 72 into clutch cylinder 96C, and the other waythrough bore passage 292, bore groove 214, and brake line 216B into theright brake cylinder 90B. At the same time, the solid land 274 ofmetering spool 200 blocks the right end of the valve passage 272preventing fluid in the inlet-outlet port 202 escaping from the orifices284 and bore groove 186 and drain 198.

In the desired way, therefore, the right clutch cylinder 96C will forcethe right clutch disk, not shown, into full engagement and the rightbrake cylinder 90B will force the right brake piston, not shown, intofully disengaged position.

FULL BRAKING, RIGHT VALVE 44--FIG. 6

The right-steer spool valve 44 affords not only a controlled way ofbraking fully on the right side, but also an assured way of braking.

For causing its controlled way of fully braking, the spool valve 44 fromits valve-in position is pulled by the lever connection 144 to its fullvalve-out position as shown in solid lines in FIG. 6. The metering spool200 follows the valve 44 part way under bias of the light spring 288 inthe spring chamber 282, thus occupying its full rightward position isshown in solid lines in FIG. 6. Because the signal pickup port 266 ofthe valve 44 is connected by the groove 224 with the drain line 226, thepickup port 266 is at drain pressure and communicates the drain pressurethrough the valve longitudinal passage 268 to the intervalve chamber270. The metering slots 286 of spool 200 are covered, blocking off theinlet outlet port 202 from line pressure, whereas the control orificesformed by the metering slots 284 and the bore passage 272 establish theinlet-outlet port 202 at the drain pressure of bore groove 186. Hence,the actual-pressure pickup port 278 communicates drain pressure throughthe longitudinal valve passage 280 and hollow interior of the hollowland 276 to the spring chamber 282.

Pressures at opposite ends of the spool 200 are thus equalized. Hence,the right brake and right clutch cylinders, not shown, empty in thatsequence through the respective brake conduit 216B and clutch conduit210C, so that the right brake, not shown, is fully spring engaged andthe right clutch pressure plate, not shown, is fully disengaged.

For causing its assured way of fully braking, the spool valve 44 in itsvalve-out position as shown in FIG. 6 has the end land 254 thereof soarranged as to uncover a reduced diameter portion of a bore groove 294with which a valve body port 296 communicates.

In actual practice, the valve body port 296 and the right-steerinlet-outlet port 202 are directly connected so as to intercommunicatethe bore grooves 204 and 294. As presently illustrated, however, aschematically shown passage 298 intercommunicates both the grooves 204and 294 and also the schematically shown passage 206 leading to theright clutch line 210C.

At all events, the right clutch line 210C is thus emptied in a pathleading from the bore groove 294, the intervalve chamber 270, thelongitudinal valve passage 268, and signal pressure pickup port, thencethrough the grooves 224 into the drain line 226. The right brake line216B communicates in much the same way except at the outset where thepath leads through the bore groove 214 and valve passage 292, so thatthe brake cylinder and clutch cylinder on the right side are fullydrained or at least assured of full drainage owing to the position ofthe end land 254 of the spool valve 44.

So even if the spool 200 for the right-steer side fails to shift intothe correct position as illustrated in FIG. 6, the steering mechanism isassured of full declutching and full braking on the tractor at thatside.

DRAG: ON BRAKE CAUSED BY VALVE 44--FIG. 7

In the illustrated position of the right-steer spool valve 44 in thisfigure, in which the corresponding system pressure will be 40 or 60 psi(3 atmospheres or 4 atmospheres), for example, the valve 44 will causepartial braking on the right side, such as for a steering turn. Hence,the signal pickup port 266 in its relation to the respective doublehelices 264 and 262 will communicate the desired signal pressure intothe intervalve chamber 270.

The metering spool 200 is shown making its final slight adjustment inthe direction of the arrow 300 into fully balanced or satisfiedposition. And, when finally adjusted into the satisfied position, themetering slots 286 forming the control orifices of the spool 200 will bebarely uncovered to allow fluid flow at a slow rate under high pressuredrop, whereas the metering slots 284 will be slightly more uncovered andallowed the same rate of flow under a smaller pressure drop leading intodrain. The chambers 282 and 270 under the actual and desired pressuresat opposite ends of the spool 200 will be essentially equalized inpressure.

SLIP CLUTCH DRIVE ON RIGHT--FIG. 8

The spool valve 44 is shown adjusted in, and the metering spool 200 isshown stabilized in, the position for partial, right-side clutchingcorresponding to an hydraulic pressure of 120 or 150 psi (8 or 10atmospheres), for example, in the system. In such valve position, thepickup port 266 of right-steer valve 44 will be communicating thedesired pressure to the end of the metering spool 200 adjacent theintervalve chamber 270. Essentially equal and opposite pressure will becommunicated by the pickup port 278 into the spring chamber 282 at theend of the spool 200 adjacent the valve plate 290. A minor, steady flowof fluid from the pressure port 164 to the drain port 188 will bemaintained by the metering spool 200 after it stabilizes so that theorifices through slots 286 provide a relatively small pressure drop asthe volume of flow makes entry into bore work passage 272, whereas thecontrol orifices through slots 284 cause a relatively large pressuredrop in the same volume of flow in passing from the passage 272 todrain.

The resulting slipping clutch drive at the right side of the tractorwill, if complemented by a full clutching drive on the left side, notshown, produce a sweeping or gradual steering turn to the right.

OPERATION: OTHER CLUTCH-BRAKE VALVE--FIG. 5

The left or second clutch-brake spool valve 44-2 and metering spool200-2 are illustrated in this figure in the full clutching position. Theaccessibility of the second bore 176-2 is essentially the same forpressure from the pressure ports 164 and 168, for drain from the conduit190, 186 and drain port 188, for drain from the spring chamber 220, sidegroove 224 and drain line 226, and for inlet-outlet pressure to be setin the left clutch and left brake from a second inlet-outlet port 302and conduit generally designated 304 leading into the conduit 210C-2 and216B-2 leading to the respective left clutch and left brake cylinders.

For the sake of brevity, a disclosure is omitted of the variouspositions of the valve elements in the second bore 176-2 for causing noclutching or braking, partial clutching, partial braking, and fullclutching and full braking on the left side of the tractor.

FOOT BRAKE SPOOL VALVE 48--FIG. 6

In reference to the brake bore 192 shown receiving it in this figure,the foot brake spool valve 48 is shown all the way in, producing nobraking. Consistent with its purpose in that valve position, and forcontrolling the right side of the tractor, the foot brake valve 48 has apair of control spools 306 and 308 which open opposite ends of the valvepassage 292, thus enabling pressure from the inlet-outlet the port 202to be freely communicated through the bore grooves 208 and 214,respectively, to the right clutch line 210C and the right brake line216B for establishing inlet-outlet pressure therein. At their respectiveshoulders adjacent the reduced diameter portion of the brake spool valve48, the spool 306 has two control slots 310 and the spool 308 has twocontrol slots 312. The valve 48 is drilled as generally indicated at 314and is vented therethrough for free movement with respect to the valveplate 290.

Control spools 316 and 318 on the valve 48 coact similarly with a valvepassage 320 which is between a bore groove 322 and a bore groove 324 soas to communicate inlet-outlet pressure for the left side of the tractorthrough the second lines 210C-2 and 210B-2 to the left side clutch andbrake. Hence, both steering brakes are held released, and the brakevalve 48 introduces braking on neither side of the tractor. However, bymodulating the inlet-outlet port pressures, which the brake valve 48 cando by progressively dumping them to drain, the brake valve can cause thebrakes to be set for various degrees of drag or be fully set, as willnow be explained.

DRAG: ON BRAKE CAUSED BY VALVE 48--FIG. 7

When, by means of the pedal connection 138, the brake spool valve 48 ispulled to a partial valve-out position as illustrated in this figure,the inlet-outlet pressure at its existing value in port 202 iscommunicated to the right clutch line 210C, and yet the clutch line 210Cbecomes isolated from the brake except through the two control slots 310in the valve control spool 306. Meantime, the brake line 216B for theright brake is opened to a considerable extent to the drain line 198through the two control slots 312 in the control spool 308 of valve 48.Hence, the right steering brake is partially applied and, for the mostpart, the right clutch releases.

The control spools 316 and 318 for the tractors left side are similarlyoperating the brake and clutch lines on the left side, namely, 210B-2and 210C-2 and, at the same time, causing the brakes on the left side todrag with partial braking. The brake is now set on the two sides of thetractor will consequently have the same pressure of partial brakeengagement even though, as illustrated in FIG. 7, the steering valvesare set differently. Hence, the left track will be clutch driven for theposition shown for the left valve 44-2, whereas the right track willhave little or no clutch drive thereupon when the right valve 44 is inthe position illustrated in FIG. 7. The tractor accordingly will slowlymake a right turn, slowly in the respect that both tracks are beingpartially braked by action of the foot brake. It is evident thegraduality or sharpness of the resulting turn will depend in part on theterrain, e.g., clay surface, gravel surface, and so forth.

Equalization between the hydraulic power brakes is insured because ofthe connection from the right brake line 216B leading in a pathincluding the bore groove 214, general drilling in the valve 48 at 314,a bore groove 326, a passage 328, a bore groove 330, thence through theleft brake line 216B-2 into the left brake cylinder, not shown.

FULL BRAKING, FOOT BRAKE VALVE 48--FIG. 8

When the brake spool valve 48 is pulled by means of the brake connection138 the and foot brake and into the full brake position as illustratedin this figure, the spool 306 of the valve 48 isolates the clutch line210C and bore groove 208 from the drain line by closing the two controlslots 310 completely at one end. The right brake line 216B and boregroove 214 on the other hand are in full communication via the borepassage 292, control slots 312, and bore groove 194 with the drain line198. Full braking in the right steering brake therefore transpires.Similarly, the pair of left control spools 316 and 318 isolate thesecond clutch line 210C-2 and communicate the second brake line 216B-2freely with the drain 226.

Hence, equalized full brake pressure is applied to both sides and thetractor is braked to a stop. In one physically constructed embodiment ofthe invention, the spool valves 48, 44, and 44-2 had a full travel of0.5 inch in order to take the full valve-out position illustrated forbrake spool valve 48 in FIG. 8. Each such valve carries a shoulder suchas the shoulder 332 illustrated on valve 48, engageable with a springseat 334 for the corresponding return spring, namely, the brake spring140 in FIG. 8. When the connection 138 is released from pull by theoperator, the return spring 140 will immedately re-expand to restore thevalve concerned, valve 48, to its in-position or normal position. Aspacer sleeve 336 between the seat 334 and a stuffing gland 338 acts asa valve stop to limit the out-travel as each valve is pulled tovalve-out position.

In operation of the steering levers 42 and 42-2 from the full clutchposition as shown in FIG. 1, the lever at one side of the vehicle can begradually rearwardly tilted by the operator so as to cause the track atthat side to become, respectively, only partially clutched, onlypartially braked, or fully braked causing a sweeping, gradual, or abruptturn of the vehicle to that side.

Or viewed the other way, in tilting the steering lever at either sidegradually fowardly, the operator causes the steering pressure at thatside to go from zero to 100 psi (7 atmospheres) in the sampleillustrated, changing the steering brake disks from full contactpressure to release, or zero contact pressure. The steering clutch atthe time is disengaged and the clutch plates are separated asillustrated and so remain to 100 psi (7 atmospheres).

Then from 100 psi to 270 psi (7 atmospheres to 18 atmospheres) internalhydraulic pressure, the pressure which immediately prior thereto forcedthe clutch plates together at that side will thereupon increase theforce from zero contact pressure to full clutching pressure.

While the tractor can be braked to a full straight stop by pulling thesteering levers 42 and 42-2 to the rear simultaneously, the simple wayintended for producing a straight full stop is by full depression of thefoot brake 46. In one physically constructed embodiment of the inventionthe brakes, under their full-stop setting, could be overcome with enginetorque only with the gearing in the highest ratio setting (low gear) andwith full power clutching.

As herein disclosed the clutch springs 98, which can be characterized aslight springs, are described as allowing the clutch piston at 50 psi (3atmospheres) to start moving and then at 100 psi (7 atmospheres) toencounter the solidness of the pressed-together clutch disks which thepiston contacts. It is evident that, if desired, the clutch springs canbe made somewhat weaker, thus allowing the clutch plates to be incontact with the clutch piston before the brake can have reached 100 psi(7 atmospheres) and have fully released. Or if the brake springs 92,which can be characterized as heavy, are made somewhat stronger, thesame effect can be made to occur whereby the clutch piston will havebrought the separated clutch plates with contact and started compressingthe clutch plates before the brake is fully released. In these ways, theoverlap whereby both the clutch and the brake are slightly engaged atthe same time on one or both sides of the tractor can be varied to suitindividual circumstances and needs.

Variations within the spirit and scope of the invention described areequally comprehended by the foregoing description.

We claim:
 1. For use in a pressure fluid system including hi pressure,lo pressure, and metered pressure outlet conduits:signal-pressuresetting valve assembly means (40) with a common bore (176) thereinhydraulically disposed for communicating with said conduits andcontrollably connecting the hi and lo pressure conduits for producing anactual metered outlet pressure in the outlet conduit in correspondencewith a signal pressure as set; first (44) and second (200) independentlyslideable members in the common bore, each having a double spool portionfor establishing the respective signal and actual pressures, and havinga pressure pickup port intermediate the double spools of each for suchsignal and actual pressures; means providing a path of flow along arestrictive orifice (262,264) of appreciable length formed along thedouble spools (252, 260) of the first member, in communication with thesignal pressure pickup port (266) thereof, said path of flow covered bycompanion sections of the bore so as to fix a generally uniform pressuregradient therealong between hi and lo pressures; means forming alongdouble spools (274, 276), of the second member a path (286, 272, 284) offlow covered by said bore and arranged to provide an actual pressure,metered output therefrom, in communication with its actual pressurepickup port (278) and with the output from said path under pressurebetween hi and lo pressures; and means for communicating (272) saidoutput under pressure to and through said metered pressure outletconduit; said members each, notwithstanding varying pickup portpressures, constantly changing positions with independent slidingmovement thereby maintaining an actual metered outlet pressure in saidoutlet conduit that is directly related to said signal pressure.
 2. Theinvention of claim 1, characterized by: one of the first and secondmembers communicating the pressure inside its pickup port to bear onboth members at their adjacent ends (254, 274) and the othercommunicating the pressure inside the pickup port to bear exclusively onthe relatively remote end (276) of one of the members.
 3. The inventionof claim 2, characterized by:the first member (44) communicating thepressure inside its signal pressure pickup port to both members at theiradjacent ends (254, 274), the second member (200) communicating thepressure inside its actual pressure pickup port to one of the members atits relatively remote end (276).
 4. The invention of claim 3,characterized by:the second member (200) communicating the pressureinside the actual pressure pickup port (278) thereof to bear exclusivelyon its own relatively remote end (276).
 5. The invention of claim 4,characterized by:heavy spring means (146) associated with the firstmember's remote end biasing the first member toward an abutting positionwith the second member at their adjacent ends; and light spring means(288) associated with the second member's remote end (276) biasing thesecond member toward an abutting position with the first member at theiradjacent ends (254, 274).
 6. For use in an hydraulic system providing apressure outlet (202) regulated thereby according to a master pressuresetting and including hi (56) and lo (D) pressure conduits:valveassembly means (40) with a common bore (176) therein hydraulicallydisposed for communicating with said conduits; a first member (44) insaid bore, independently slideable therein and having a double spoolportion (252, 260); means forming a restrictive orifice (262, 264) ofappreciable length along the double spools and covered by companionsections of the bore (176); means (182), 224) to communicate the borewith the hi and lo pressure conduits for applying specified pressure tosaid first member at points causing flow of hydraulic fluid through saidorifice from one end portion to another so as to fix a pressure againsttherealong between hi and lo; a pressure setting takeoff (266) in saidfirst member connected between a first end (254) of the latter and acommunicating point on the double spool portion which intervenes (at266) so as to divide the double spools and to divide the restrictedorifice into two oppositely extending sections maintaining the pressuregradient from hi to lo; master setting means (42) to which the firstmember is mechanically secured for longitudinally adjusting the relativeposition of the first member in said bore and consequently the relativeposition of the pressure setting takeoff (266 between the orificesections) and the covering sections of the bore; means forming, along aregulator valve member (200) in said common bore, a path (286) of flowarranged to provide an output therefrom, and with the output from saidpath under pressure between hi and lo; and means for communicating (272)said output under pressure to and through said regulated pressure outlet(202), said regulator valve member in the common bore being likewiseindependently slideable therein with respect to, but adjacent to saidfirst end of said first member and together having an adjacent pressuresensitive end area in communication with the master setting pressure toafford regulated pressure output according to the master pressuresetting.
 7. For use in a hydraulic system providing a pressure outlet(202) regulated thereby according to a master pressure setting andincluding hi (56) and lo (D) pressure conduits;valve assembly means (40)with a common bore (176) therein hydraulically disposed forcommunicating with said conduits; means forming, along a firstindependently slideable member (44) in said common bore, a restrictedorifice (262, 264) of appreciable lengths; means (182, 224) forcommunicating said bore with the hi and lo pressure conduits forapplying specified pressure-causing flow of hydraulic fluid through theorifice from one end portion to another so as to fix a pressuredifferential therealong between hi and lo; master setting means (42) towhich the first member is mechanically secured for relativelylongitudinally adjusting the position of the first member and bore;means (286) forming, along a regulator valve member (200) in said commonbore, which is independently slideable therein with respect to the firstmember, a path of flow arranged to provide an output pressure therefrombetween hi and lo, said regulator valve member having at least the endthereon adjacent to the first member provided with a pressure sensitiveend area for regulating the regulator valve member therewith; means(272) for communicating said output under pressure to and through saidregulated pressure outlet (202); and means (268) for communicating themaster setting pressure to the pressure sensitive end area of theregulator valve member adjacent the first member to afford a pressureoutlet regulated according to said master pressure setting.
 8. Theinvention in accordance with claims 6 or 7, characterized by:meansproviding a pull connection (144) mechanically securing the mastersetting means to the first slideable member for adjusting the latter ina direction of pull, away from the adjacent regulator valve member; anda strong valve return spring (146) biasing the first slideable member inthe opposite direction.